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Reliability issues with VTL amps/pre-amps

I have a VTL ST-85 which I use mostly, in the triode mode. The left channel tubes have blown 5 times in a two year period. I had repairs and the tube compliment replaced by VTL during this time. After all the shipping costs, VTL replaced the last set of tubes for free and all is fine for now, but I'm worried it will blow again. No one at VTL has ever told me why they keep blowing. Has anyone had similar experiences with VTL? Is this type of problem common with their products?
128x128tarraga
pryso
1,915 posts
 
I've owned a pair of older VTL 300s for at least a dozen years. While they have had little use in the past couple of years they have been very reliable. They had one part failure which VTL replaced for free even though I was not the original owner.

I agree they are among the best sounding and most reliable of the big tube amps.
microstrip
180 posts
 
If you look at VTL schematics you will see they are very simple and intrinsically reliable, operating the output tubes at low current. However they use a high anode voltage and the choice of output tubes is critical - if you take Albert Porter recommendation of Wing C 6550 you will have no problems!
Many cheap 6550 can not withstand these high voltages. Also, when tubes became tired replace them - do not wait until they break!
tarraga's avatar
tarraga OP
15 posts
 
Thanks for all your input. I do love the sound of this amp. I have used only tubes supplied by VTL and Bea Lam has been very helpful in this regard. However, I still have no answer as to why, other than the tubes were bad. Perhaps quarterly biasing will help (as ryriken has suggested).

It does have a triode/tetrode switch and really sounds better, in my system, in the triode mode. I am using a Melos MA-110 pre-amp, B & W Matrix I speakers, a Meridian 200 transport and 203 processor, A Rega P3 TT w/a Project Tubebox SE. I've recently added a Paradigm sub (but this has been added after I got the amp back from VTL, not during the problematic period).
lissnr
365 posts
 
Until recently I've been a VTL MB-125 owner with tremendous satisfaction. It uses EL-34's (4 per mono bloc)and I've used both JJ's and Electro Harmonics with no troubles at all. I used them for over 6 years and averaged about 30-50 hours a week. Never a reliability issue. I would check the bias every month or so and they almost never drifted or needed much adjustment at all. Be sure you never switch between tetrode/triode with it on, of course, but other than that they are just outstanding products with awesome sound [and superb] reliability. I hope your ST-85 has finally "settled down". Best of luck.
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